The top level directory contains a clone file and subdirectories numbered from zero to the number of connections configured. Opening the clone file reserves a connection. The file descriptor returned from the open(2) will point to the control file, ctl, of the newly allocated connection. Reading the ctl file returns a text string representing the number of the connection.

A connection is controlled by writing text strings to the associated ctl file. After a connection has been established data may be read from and written to the data file.

The SSL protocol provides a stream connection that preserves read/write boundaries. As long as reads always specify buffers that are of equal or greater lengths than the writes at the other end of the connection, one write will correspond to one read.

Options are set by writing control messages to the ctl file of the connection.

The following control messages are supported:

fd open-file-descriptor

Run the SSL protocol over the existing file descriptor.

alg cryptoalgs

Connections start in alg clear which means no encryption or digesting. Writing alg sha to the control file turns on SHA-1 digest authentication for the data channel. Similarly, writing alg rc4_128 enables encryption. Both can be turned on at once by alg sha rc4_128. The digest mode sha may be replaced by md5. The encryption mode rc4_128 may be replaced by rc4_40, rc4_128, rc4_256, des_40_ecb, des_40_cbc, des_56_ecb, and des_56_cbc. The mode may be changed at any time during the connection.

secretin base64-secret

The secret for decrypting and authenticating incoming messages can be specified either as a base64 encoded string by writing to the control file, or as a binary byte string using the interface below.

secretout base64-secret

The secret for encrypting and hashing outgoing messages can be specified either as a base64 encoded string by writing to the control file, or as a binary byte string using the interface below.

Before enabling digesting or encryption, shared secrets must be agreed upon with the remote side, one for each direction of transmission, and loaded as shown above or by writing to the files secretin and secretout. If either the incoming or outgoing secret is not specified, the other secret is assumed to work for both directions.

The encryption and hash algoritms actually included in the kernel may be smaller than the set presented here. Reading encalgs and hashalgs will give the actual space-separated list of algorithms implemented.